This invention has particular application to four wheel drive vehicles wherein the front wheels or the rear wheels are engaged to be driven by the drive train only as required. For purposes of discussion, the front wheels will be referred to as the set of wheels that are selectively engaged to be driven by the drive train. A transfer case coupled to the transmission has suitable gearing to be engaged or disengaged as needed by simply shifting a lever. The engagement of the transfer case gearing supplies power to the front drive train which will drive the front wheels. It is of course desirable to be able to engage the front wheels with the front drive train when the front drive train is under power and to disengage the wheels when the front drive train is idle. The disengagement of the front wheels from the drive train prevents forced rotation of the drive train as a result of the front wheels being driven as the vehicle is propelled.
It will thus be appreciated that in the example given there are two positions in the drive train whereat a connect/disconnect mechanism is required. This invention may be applicable to both positions as well as to other positions of connect/disconnect components that may exist in alternate design configurations. For purposes of explanation, the invention will hereafter be considered for application between a front wheel axle and the corresponding front wheel hub.
Generally, an axle of the drive train, a clutch ring and wheel hub (on which a wheel is mounted) are concentrically mounted to the vehicle. The axle is received within the clutch ring and the clutch ring is in turn received within the hub. A non-circular form such as splines or teeth, hereafter referred to as splines, are provided on the periphery of the axle, on the interior and exterior of the clutch ring and on the interior of the hub. The clutch ring splines are engaged at all times with either the splines of the axle or splines of the wheel hub. The clutch ring is axially movable along the concentric axis to be in engagement with both members or to be in engagement with only one member. The clutch ring moved to engagement with both members "locks" the wheel hub and the drive axle rotatively to each other.
A shift mechanism is provided for moving the clutch ring axially along the concentric axis to a position of engagement with both the drive axle and the hub and to a position where the clutch ring is engaged with only one of the members. The clutch ring is moved along the splines of the member to which it is permanently engaged.
One of the problems encountered with this arrangement is in moving the clutch ring to a position to be engaged with both members. Rarely are the splines of the clutch ring and the splines of the other member aligned to permit ready engagement. Thus the shift mechanism incorporates a biasing member, such as a spring, which is compressed and which affects movement of the clutch ring when the splines of the clutch ring and the splines of the engageable member become aligned. When torque is applied, that is when the axle and hub are rotated relative to each other, the splines will become momentarily aligned and the compressed spring will urge the clutch ring into engagement. The continuously applied torque and the urging of relative rotation will however create a frictional force between the engaging splines that exceeds the biasing force of the spring thus limiting the engagement of the splines of the clutch ring and the engageable member to a small degree of overlap.
The driving torque as between the axle and the wheel is applied only at the overlap of the splined ends which is minimal. This minimal overlap has been largely successful, however repeated shifting of the clutch ring under these conditions will eventually wear away the ends of the splines which will result in chattering or prevent engagement of the clutch ring with the engageable member.
The above problem of shifting the clutch ring into engagement exists with either the manual or automatic actuation of a hub clutch interlock and at any position in the drive train where interlock is achieved while the drive component is rotating and under torque. The problem of the interlock was initially resolved for a cam actuated automatic hub lock and further problems were encountered and resolved with respect to that specific application. As concerns the cam actuated interlock system of the illustrated embodiment, a fixed cam is provided that is non rotative with respect to either the axle or the hub. A cam follower which is movable axially to affect movement of the clutch ring is mounted on the axle in a non-rotative but sliding manner. A biasing spring is disposed between the cam follower and the clutch ring. Upon rotation of the axle, the cam follower is forced to move axially along the axle, thus urging the clutch ring into the engaged position via the spring disposed between the follower and the clutch ring. As was previously described, engagement occurs upon alignment of the splines of the clutch ring and the splines of the engageable member. An opposing spring is provided to urge the clutch ring out of engagement when rotative torque is no longer applied to the axle.
As simple as the above sounds, there are a number of components required to successfully perform this operation. A moving cam member is provided that is mounted strategic to the fixed cam and cam follower. The moving cam member urges further movement of the cam follower and maintains the cam follower separated from the fixed cam. The moving cam must rotate, but in order to perform the function must have a resistance to rotation. This has been accomplished by a complex yieldable braking mechanism that is expensive and subject to rapid wearing.
In a more specific form of automatic actuation, where the clutch ring is permanently splined to the wheel hub, the cam follower does not simply act against the actuating spring. A cage member is provided that encloses the actuating spring and the clutch ring. The spring is compressively movable within the cage and the clutch ring is slidably moveable within the cage. The cage has legs or rails that extend through the tooth form of the splines of the clutch ring and are connected to the opposite end of the cage.
The opposite end of the cage engages the spring that is provided to urge the clutch ring out of engagement. Movement of the cam follower to affect engagement of the clutch ring thus forces movement of the cage to compress the opposing spring to eliminate its resistive force. The cage applies a force to the clutch ring via the engaging spring to urge the clutch ring into engagement. The spring will of course compress if the splines of the clutch ring and the axle are out of alignment. The other end of the cage (on the other side of the clutch ring) engages the opposing spring and compresses the opposing spring to eliminate the resistance of the opposing spring and allow a more rapid movement of the clutch ring when the gear splines are aligned.
The cage member rotates with the clutch ring and during periods of engagement and disengagement, there is relative rotative movement as between the cam follower and cage end and this relative movement applies a torque at the point of connection as between the end of the cage in abutment with the cam follower and the rails of the cage that extend to the other end. Heretofore the cage has been constructed in a manner which required a snap fit connection of the rails to the end of the cage in abutment with the cam follower and that snap fit connection, being subjected to the rotative torque, would frequently break.